We've seen how the atmosphere affects the oceans. Now,
how do the oceans affect the atmosphere? Remember, we said this was a "dynamic
duo." The oceans are main reservoirs of readily available
carbon
dioxide (CO2), an important
greenhouse gas. The cold, deep water in the
ocean is the main reservoir of dissolved CO2. TRY THIS: Shake a hot can of
coke and open it. Shake a cold can of coke and open it. What happened? What
does this experiment demonstrate? Need I say more? (Check the activity page
for an explanation of the demonstration.)

The oceans carry heat from the tropics, that's the area
near the equator, to the higher latitudes, the area near the poles, to maintain
Earth's temperature. They also take carbon dioxide and hide it from the atmosphere.
Here's how it happens. Sunlight warms the surface of the ocean in the tropics.
Wind-driven surface currents carry the heat toward the poles. In the North
Atlantic, the warm currents from the tropics feed the North Atlantic Current
shown in red in the figure. As the current flows northward toward Norway and
Greenlamd, it loses heat to the atmosphere and cools down. In winter the water
near Norway and Greenland gets so cold and dense it sinks all the way to the
bottom of the ocean. The cold bottom water feeds bottom currents shown in
blue and green. Eventually, mixing brings the bottom water back to the surface
in other parts of the ocean, sometime as far away as the North Pacific. When
the water gets to the surface, sunlight warms the water, and the cycle starts
over.

The deep circulation shown in the picture is important
for two reasons:

Cold water carries carbon dioxide deep into the ocean, taking it away
from the atmosphere and...

Surface currents that sink and feed deep currents carry much more heat
toward Europe than currents that stay on the surface. As a result, Norway
at 60 degrees is far warmer than southern Greenland and northern Labrador
which are at the same latitude.